Check dependencies for a compatible C++ stdlib

There are now a few possible C++ standard libraries a given build could
be using, with subtle incompatibilities and possibility of breakage
when mixed. This makes sure that the dependency chain was compiled in
a compatible manner.

Fortunately all of the Apple compilers use the same libstdc++, and we
don't yet support building with libc++, so this will primarily only
nag users trying to use GNU gcc who already have software installed
with Apple compilers.

Future TODOs:

* Add general support for building with libc++ (compatibility checking
  already handled here)
* Possibly track formulae which actually build C++ bindings, so that
  users aren't bothered by spurious nagging re: interpreted languages,
  pure-C software, etc.

Library/Homebrew/build.rb

@@ -13,6 +13,7 @@ at_exit do
 end
 
 require 'global'
+require 'cxxstdlib'
 require 'debrew' if ARGV.debug?
 
 def main
@@ -148,6 +149,14 @@ class Build
       end
     end
 
+    # We only support libstdc++ right now
+    stdlib_in_use = CxxStdlib.new(:libstdcxx, ENV.compiler)
+
+    # This is a bad place for this check, but we don't have access to
+    # compiler selection within the formula installer, only inside the
+    # build instance.
+    stdlib_in_use.check_dependencies(f, deps)
+
     f.brew do
       if ARGV.flag? '--git'
         system "git init"
@@ -170,7 +179,7 @@ class Build
 
         begin
           f.install
-          Tab.create(f, ENV.compiler,
+          Tab.create(f, :libstdcxx, ENV.compiler,
             Options.coerce(ARGV.options_only)).write
         rescue Exception => e
           if ARGV.debug?

Library/Homebrew/exceptions.rb

@@ -112,6 +112,21 @@ class UnsatisfiedRequirements < Homebrew::InstallationError
   end
 end
 
+class IncompatibleCxxStdlibs < Homebrew::InstallationError
+  def initialize(f, dep, wrong, right)
+    super f, <<-EOS.undent
+    #{f} dependency #{dep} was built with the following
+    C++ standard library: #{wrong.type_string} (from #{wrong.compiler})
+
+    This is incompatible with the standard library being used
+    to build #{f}: #{right.type_string} (from #{right.compiler})
+
+    Please reinstall #{dep} using a compatible compiler.
+    hint: Check https://github.com/mxcl/homebrew/wiki/C++-Standard-Libraries
+    EOS
+  end
+end
+
 class FormulaConflictError < Homebrew::InstallationError
   attr_reader :f, :conflicts
 

Library/Homebrew/formula_installer.rb

@@ -1,5 +1,6 @@
 # encoding: UTF-8
 
+require 'cxxstdlib'
 require 'exceptions'
 require 'formula'
 require 'keg'
@@ -94,6 +95,17 @@ class FormulaInstaller
       raise "Unrecognized architecture for --bottle-arch: #{arch}"
     end
 
+    if pour_bottle? true
+      # TODO We currently only support building with libstdc++ as
+      # the default case, and all Apple libstdc++s are compatible, so
+      # this default is sensible.
+      # In the future we need to actually provide a way to read this from
+      # the bottle, or update the default should that change
+      # at some other point.
+      stdlib_in_use = CxxStdlib.new(:libstdcxx, :clang)
+      stdlib_in_use.check_dependencies(f, f.deps)
+    end
+
     oh1 "Installing #{Tty.green}#{f}#{Tty.reset}" if show_header
 
     @@attempted << f